🌡️ °C to °Ré — Celsius to Réaumur Converter

Convert Celsius to Réaumur. Historical scale once used across Europe for wine-making and brewing.

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Formula °Ré = °C × 4/5

All Celsius conversions

Unit	Name	Value
°F	Fahrenheit	33.8
K	Kelvin	274.15
°R	Rankine	493.47

Related Temperature conversions

°F → °C °C → K K → °C °F → K

⚡ How to Convert Celsius to Réaumur

Formula: °Ré = °C × 4/5. Enter any value in the converter above for an instant result. Reverse formula available via the swap button.

Worked Examples

Example 1 — Water freezing point

Apply formula: °Ré = °C × 4/5 with value 0

The freezing point of water (0°C / 32°F / 273.15 K / 0°Ré / 491.67°R) is a universal reference point. Converting it between °C and °Ré confirms the formula and provides a sanity check for any temperature conversion.

Example 2 — Water boiling point

Apply formula: °Ré = °C × 4/5 with value 100°C equivalent

The boiling point of water at sea level (100°C / 212°F / 373.15 K / 80°Ré / 671.67°R) is the upper calibration anchor for the Réaumur scale and a key reference in all temperature conversions.

Example 3 — Human body temperature

Apply formula: °Ré = °C × 4/5 with 37°C equivalent

Normal human body temperature (37°C / 98.6°F / 310.15 K / 29.6°Ré) appears frequently in historical medical texts. Historians and medical historians converting these values for modern analysis use this conversion.

Example 4 — Historical scientific reference

Apply formula: °Ré = °C × 4/5 to historical data

18th-century European scientists including Fahrenheit, Celsius and Lavoisier often referenced Réaumur values in correspondence and papers. Historians translating these to modern scales for comparative analysis use this converter.

Celsius to Réaumur — Reference Table

Celsius (°C)	Réaumur (°Ré)	Real-world context
−273.15°C equivalent	0 K / −273.15°C / 0°Ré	Reference point
0°Ré	273.15 K / 0°C / 0°Ré / 491.67°R	Water freezing point
20°C equivalent	Room temperature equivalent	Comfortable indoor temperature
37°C equivalent	Body temp: 37°C / 98.6°F / 310.15 K / 29.6°Ré	Human body temperature
80°Ré / 100°C equivalent	80°Ré = 100°C = 212°F = 373.15 K	Water boiling point (Réaumur upper anchor)

Mental Math Tricks for °C ↔ °Ré

Remember the Réaumur boiling point is 80°Ré

Unlike Celsius (100°) or Fahrenheit (212°), the Réaumur scale goes to 80° at boiling. This 4/5 ratio to Celsius (°C × 4/5 = °Ré) is the key to all Réaumur conversions.

Convert via Celsius as an intermediate step

If you know the Celsius equivalent, converting to/from Réaumur is simplest: °Ré = °C × 4/5, or °C = °Ré × 5/4. Use Celsius as the bridge for °C to °Ré via two familiar steps.

Réaumur zero = Celsius zero

Both scales share the same zero point (water freezing). Only the degree size differs: 1°Ré = 1.25°C = 2.25°F.

Historical context check

Réaumur values for everyday temperatures (0–40°Ré) correspond to 0–50°C. If a historical text mentions a summer temperature of 24°Ré, that is 30°C (86°F) — a hot day.

Who Uses This Conversion?

Real professions and situations that need °C to °Ré conversion

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Historians of Science

Réaumur was standard in French, German and Russian scientific literature from 1730–1880. Historians reading papers by Lavoisier, Fahrenheit or early Russian academicians convert Réaumur temperatures to modern scales for analysis and publication.

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Literary Scholars

Russian literature (Tolstoy, Turgenev) and 18th-century French novels reference Réaumur temperatures. Literary scholars and translators convert these for annotated editions accessible to modern readers.

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Traditional European Brewers

Some traditional German and Austrian wine and beer-making practices still reference Réaumur temperatures in fermentation guides inherited from 19th-century manuals. Brewers converting to modern Celsius thermometers use this.

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Science History Students

Students studying the history of thermometry and metrology encounter Réaumur values in primary sources. Converting them to familiar Celsius or Kelvin values helps contextualise 18th-century scientific achievements.

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Archival Researchers

Temperature data in European scientific archives, meteorological records and natural history collections from before 1900 is often in Réaumur. Researchers digitising and standardising this historical data convert to Celsius for modern databases.

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Museum Curators & Conservators

Historical scientific instruments (Réaumur thermometers) in museum collections are documented with period-accurate temperatures. Curators converting calibration marks to Celsius for educational labels and conservation environment monitoring use this converter.

All Celsius Conversions

Frequently Asked Questions

Use the formula: °Ré = °C × 4/5. The converter above handles this automatically.

Use the formula °Ré = °C × 4/5 with the value 0 to get the result. Enter 0 in the converter above for the exact answer.

The Réaumur scale was invented by French scientist René Antoine Ferchault de Réaumur in 1730. He set 0°Ré at water's freezing point and 80°Ré at boiling, based on the expansion ratio of his alcohol thermometers.

Réaumur is largely obsolete today, but appears in historical scientific texts, 18th–19th century European literature, and some traditional brewing contexts in Germany and Austria.

Enter 100 in the converter above to get the exact result using the formula °Ré = °C × 4/5.

The conversion formula is: °Ré = °C × 4/5. The two scales share the same zero point for water freezing (where applicable) but use different degree sizes.

This conversion is primarily needed by historians studying 18th–19th century European scientific literature, researchers reading historical texts in French, German or Russian, and academics in the history of science.

About Celsius and Réaumur

Celsius (°C)

The Celsius scale is the internationally recognised standard for this temperature range.

See the dedicated °C converter pages for full historical details.

Réaumur (°Ré)

The Réaumur scale (symbol: °Ré) was proposed by French scientist René Antoine Ferchault de Réaumur in 1730. He defined 0°Ré as the freezing point of water and 80°Ré as the boiling point — making 1°Ré equal to 1.25°C. The choice of 80 degrees was based on his observations of alcohol thermometers expanding by 8/1000 of their volume between these two points.

Once widespread across continental Europe, the Réaumur scale was used in France, Germany, Russia and Italy until the late 19th century. Notably, Leo Tolstoy references Réaumur temperatures in War and Peace (1869), and early German chemistry papers by Justus von Liebig use it. Today it is obsolete in all practical applications, though it appears in historical scientific texts and some wine-making traditions in Germany and Austria.

Common use: Réaumur-based conversions are primarily of academic, historical and archival interest today. The scale is obsolete in science and industry but persists in 18th–19th century European literature, historical scientific records and some traditional wine and brewing contexts.